DONALD Trump has been accused of lying in a bitter back-end-forth over his phone call with the pregnant widow of a fallen American soldier.

Sergeant La David Johnson was among four soldiers killed in an ambush in Niger on October 4. A photo of his wife Myeshia draped over his coffin broke America's heart earlier this week.

On Tuesday Mr Trump called Ms Johnson to offer his condolences. At the time, she was reportedly riding in a limousine with Sgt Johnson's mother, Cowanda Jones-Johnson, and a Democratic Congresswoman, Frederica Wilson.

Afterwards, Ms Wilson publicly accused the president of disrespecting Sgt Johnson during the call.

The widow of Sgt. La David Johnson hugs the casket carrying his remains. He was among 4 killed in #Niger Heartbreaking - God Bless her. pic.twitter.com/6GxLOh0iiJ

"She was crying the whole time, and when she hung up the phone, she looked at me and said, 'He didn't even remember his name.' That's the hurting part," Ms Wilson told MSNBC, saying she heard Mr Trump's call on speakerphone.

"He said ... something to the effect that, 'He knew what he was getting into when he signed up, but I guess it hurts anyway.' You know, just matter-of-factly, that this is what happens, anyone who is signing up for military duty is going to die. That's the way we interpreted it. It was horrible. It was insensitive. It was absolutely crazy, unnecessary. I was livid."

In response, Mr Trump accused Ms Wilson of lying about the conversation.

"Democratic Congresswoman totally fabricated what I said to the wife of a soldier who died in action (and I have proof). Sad!" he tweeted.

Democrat Congresswoman totally fabricated what I said to the wife of a soldier who died in action (and I have proof). Sad!

"I didn't say what that congresswoman said, didn't say it at all. She knows it, and she now is not saying it," Mr Trump claimed, with his arms crossed.

"I had a very nice conversation with the woman, with the wife who sounded like a lovely woman. Did not say what the Congresswoman said, and most people aren't too surprised to hear that.

"I did not say what she said, and I'd like her to make the statement again because I did not say what she said."

Asked what his "proof" was, as mentioned in his tweet, Mr Trump said: "Let her make her statement again and then you'll find out. OK. Let her make her statement again and then you'll find out."

Ms Wilson did indeed make the statement again, this time on US panel show The View.

"President Trump is a liar ... If he was taping the conversation, bring it on!" she said. The White House has since clarified that the conversation was not taped, so if Mr Trump does have proof, that isn't it.

Congresswoman Frederica Wilson. Pic: AP

Meanwhile, Sgt Johnson's mother Cowanda, who was also present during the call, told The Washington Post Ms Wilson's account of the conversation was in fact accurate.

"President Trump did disrespect my son and my daughter and also me and my husband," Ms Jones-Johnson said, declining to elaborate further.

Myeshia Johnson met her husband when she was six years old, according to US media. She is due to give birth in January and already mother to Johnson's surviving two-year-old son and six-year-old daughter, Miami Station WPLG reports.

Emotional pictures from the airport show her draped over his casket, with her daughter nearby.

Sgt. La David Johnson. Pic: AFP

The timing of this spat is particularly awkward, given Mr Trump boasted on Tuesday about his outreach to the families of fallen soldiers. He claimed former presidents, such as Barack Obama, George W. Bush and Bill Clinton, did not call every family.

"I think I've called every family of someone who's died," Mr Trump said.

He cited the death of White House chief of staff John Kelly's son in Afghanistan. Kelly was a Marine general under Obama when his Marine son Robert died in 2010.

"You could ask General Kelly, did he get a call from Obama?" Mr Trump said on Fox News radio.

President Donald Trump. Pic: AP

However families came forward to dispute Mr Trump's claim, with Sheila Murphy saying she heard nothing when her son died in Syria in May, even after writing to Trump saying "some days I don't want to live".

Today Whitney Hunter, whose husband Jonathon died in Afghanistan told CNN she was promised a call from Mr Trump but it never came. She spoke to Vice President Mike Pence instead.

"I don't like that I was told that I would receive the phone call but then I never did," Ms Hunter said.

And according to the Washington Post, one of the calls Mr Trump did in fact make was equally disappointing. Mr Trump reportedly offered $25,000 to a grieving father in financial difficulty and promised to establish an online fundraiser - but didn't follow through on either idea.

Chris Baldridge, whose son Corporal Dillon Baldridge died on June 10, told the newspaper he received a letter from Mr Trump, but no cheque. However the White House claims a cheque was sent to him.

"It's disgusting that the media is taking something that should be recognised as a generous and sincere gesture, made privately by the President, and using it to advance the media's biased agenda," said spokeswoman Lindsay Walters.

There is also plenty of proof Barack Obama and George W. Bush - saddled with far more combat casualties than the roughly two dozen so far under Mr Trump, took painstaking steps to write, call or meet bereaved military families.

Democrats and some former government officials were livid, accusing Mr Trump of "inane cruelty" and a "sick game".

Democratic Sen. Tammy Duckworth of Illinois, an Iraq veteran who lost both legs when her helicopter was attacked, said: "I just wish that this commander in chief would stop using Gold Star families as pawns in whatever sick game he's trying to play here."